The invention relates to fluid dispensers, and in particular, to a constant pressure fluid dispenser for dispensing viscous fluids such as a molten hot melt adhesive intermittently.
In the deposition of a viscous fluid such as molten hot melt adhesive it is generally desirable to deposit the fluid in a uniform fashion. In the case of depositing a bead of adhesive in an intermittent fashion, it is desirable that each bead be consistent. Earlier equipment such as automatic hot melt dispensing guns Models AD-24 and H-20 manufactured by Nordson Corporation of Amherst, Ohio have done a satisfactory job in the intermittent deposition of a bead of molten hot melt adhesive. However, fluid pressure at the dispensing orifice is higher when the dispenser is not dispensing since the system is at a maximum output pressure so that at the commencement of each separate deposit an associated pressure drop occurs as the system is opened to atmospheric pressure. The consequence thereof being that an undesirably large bead of adhesive or "snake head" is initially deposited.
Experience has also shown that other factors can cause or contribute to the deposition of snake heads. These factors include changes in the fluid viscosity and fluid temperature, and changing of the dispensing orifice size due to clogging.
In many applications the deposition of snake heads is not desirable. Thus, it would be desirable to provide an improved fluid dispenser that dispenses viscous fluid in an intermittent fashion without experiencing pressure drops at the commencement of each separate deposit and pressure surges within the system at the finish of each deposit.